The present invention relates to an infusion apparatus for use with an infusion bag containing an infusion liquid, which comprises and/or is connectable with a conduit means for transport of infusion liquid to a patient, the infusion apparatus being of a type which comprises:
a first space in which the infusion bag is intended to be disposed,
a second space of variable volume provided with an inlet through which a pressure generating liquid is supplied to the second space to change its volume, the first and second spaces being so arranged that the pressure generating liquid, by said change of volume, exerts a pressure on the infusion bag in the first space to make the infusion liquid leave the infusion bag via the conduit means. An infusion apparatus of this kind is known from U.S. Pat. No. 5,348,539. This document describes an infusion apparatus with a suitable space for comprising an infusion bag. A second space abuts the infusion bag. Into this second space a liquid, for instance, can be introduced by means of a pump system. When the liquid is introduced into the second space, the second space exerts a pressure on the infusion bag. Thereby infusion liquid is conducted out from the infusion bag. In order to supply a liquid to the second space the apparatus comprises a pump or relatively complicated design. Furthermore the apparatus comprises an electrically controlled control device. The apparatus, in addition, comprises various sensors. In case of excessive pressure in the second space the pump motor is switched of.
WO 96/13288 describes an infusion pump preferably driven by air. Alternatively a liquid can be used. A pump pumps air to a bladder which exerts pressure on an infusion bag. The apparatus also comprises a pressure sensor and a monitoring circuit.
The apparatus described in the aforementioned documents are of relatively complex design and comprise monitoring circuits and pressure sensors.
It is also known in health care that infusion liquid can be supplied to a patient directly from an infusion bag. In this case the infusion bag is placed on a higher level than the patient. By means of a tube originating at the infusion bag infusion liquid is transported by gravitation to a cannula connected to the patient. Such an arrangement often comprises a controllable clip arrangement attached to a tube to control the flow rate of the infusion liquid. The apparatus can also comprise a drip chamber to visualise the flow rate. With such an apparatus it is difficult to precisely control the flow rate of the infusion liquid.
In connection with infusion apparatus often relatively expensive disposable components have to be used.
In health care a large number of infusions are given. In certain infusions of such kind it is very important that the infusion liquid be supplied to the patient at a precisely controlled flow rate. When, for instance, certain drugs are administered to a patient by infusion it is often necessary to control the dosage precisely. Furthermore it is advantageous if the flow rate of the infusion liquid is independent of the relative height level of the infusion bag in respect of patient.
An object of the present invention is to provide an infusion apparatus which can be used with infusion bags containing an infusion liquid; the infusion apparatus should be relatively simple and cheap to manufacture while, at the same time, operating with a high degree of safety. Another object of the invention is that the infusion apparatus should be able to transport infusion liquid to a patient at a well-controlled flow rate. A further object of the invention is to avoid the use of expensive disposable components in connection with the infusion apparatus.
These objects of the invention are provided by an infusion apparatus of the kind disclosed in the introduction, the apparatus being characterised by comprising a closing means of a form and disposition to abut against and exert a load on the conduit means in such a manner that the infusion liquid does not flow out from the infusion bag when the pressure generating liquid is not exerting a pressure on the infusion bag, while said load diminishes when the pressure generating liquid is exerting a pressure on the infusion bag to make infusion liquid leave the infusion bag via the conduit means if the pressure generating liquid exerts at least a certain minimum pressure on the infusion bag.
When a pressure of a certain size is exerted on the infusion bag the load of the closing means on the conduit means thus decreases while infusion liquid leaves the infusion bag via the conduit means. An increase in pressure on the infusion bag results in a state of equilibrium which causes infusion liquid to be transported to the patient at a well-controlled flow rate. This makes the height level of the infusion bag in relation the patient to lack effect on the flow rate. It should be noted that the closing means might abut a tube extending from the infusion bag to the patient. It is also possible for the closing means to abut an outlet area forming a part of the infusion bag proper. In this patent application the term xe2x80x9cinfusion liquidxe2x80x9d shall be understood in a broad sense and thus comprises, for example, also liquid or material carried in a liquid which is given to a patient by tube-feeding. The term also comprises blood which is given in blood transfusion.
According to a preferred embodiment of the invention the infusion apparatus comprises a supporting means arranged to abut the infusion bag when the infusion bag is disposed in the first space, the supporting element being arranged in such a way that, when the pressure generating liquid is exerting a pressure on the infusion bag the infusion bag will exert a pressure on the supporting means, the infusion apparatus comprising a connecting element for connecting the supporting means with the closing means, to make the load exerted by the closing means on the conduit means decrease when the infusion bag is exerting a pressure on the supporting means. Thus an increase of pressure on the infusion bag contributes, by assistance of the supporting means, to decrease the load of the closing means on the conduit means. This contributes to a state of equilibrium being reached between the pressure of the infusion liquid and the load on the closing means at a relatively small increase of pressure on the infusion bag. This results in the flow rate of the infusion liquid to the patient to be controlled with very high precision.
According to a further embodiment of the invention the closing means comprises a first portion and a second portion which, in combination, abut resiliently against and exert a load on the conduit means in such a manner, that the conduit means is clamped between the first and second portions while the connecting element connects the supporting means and the first portion in such a way that, when the pressure on the supporting means increases, the first portion is affected to move in a direction away from the second portion while the load exerted by the first and second portions on the conduit means decreases. This embodiment is a technically simple and well functioning application of the invention.
According to still another embodiment of the invention the infusion apparatus comprises a third space arranged to contain pressure generating liquid, the third space being connected with the second space by joining means for transport of the pressure generating liquid from the third space to the second space. Thus the infusion apparatus comprises the pressure generating liquid; therefore it is not necessary to supply this liquid to the infusion apparatus from an external source.
According to a further embodiment of the invention the connecting means comprises a drip chamber which allows visual control of the pressure generating liquid transported from the third to the second space. A person supervising the infusion apparatus thus can see by his/her own eyes at which flow rate the pressure generating liquid is being transported to the second space. Thereby an indication is indirectly obtained in regard of at what rate the pressure is being built up in the second space.
According to a further embodiment of the invention the infusion apparatus is designed in such a way, that, when the pressure generating liquid exerts a pressure on the infusion bag of a size that makes the infusion liquid leave the infusion bag via the conduit means, the flow rate of the pressure generating liquid in the drip chamber will correspond to the flow rate of the infusion liquid in the conduit means. This makes the visual control of the flow rate of the pressure generating liquid to constitute, at the same time, a visual control of the flow rate of infusion liquid to the patient. Thus the drip chamber can be arranged permanently in the infusion apparatus in a closed system for transport of pressure generating liquid from the third to the second space. Thus there is, for instance, no need for a further drip chamber to be arranged at the conduit means leading to the patient.
According to still a further embodiment of the invention the connecting means comprises a flow rate regulator to control the flow rate of the pressure generating liquid to the second space. Thereby the flow rate of the pressure generating liquid can be controlled with a high degree of precision. This makes the flow rate of the infusion liquid also to be controllable with precision.
According to still a further embodiment of the invention the connecting means comprises a pressure regulator disposed between the third space and the flow rate regulator to provide a constant pressure in the pressure generating liquid present at the side of the flow speed regulator to which pressure generating liquid is supplied from the third space. The existence of such a constant pressure does not change the flow rate of the pressure generating liquid provided that the flow rate regulator setting is not changed. A pressure regulator of this kind thus contributes to maintain a well-controlled flow rate of the infusion liquid.
According to a further embodiment of the invention the infusion apparatus comprises pressure generating means to generate a pressure at the pressure generating liquid present in the third space. Thereby a pressure of the pressure generating liquid thus can be built up. As a pressure generating means a hand-driven air pump can be used, for instance. The pressure generated in the pressure generating liquid in the third space should be high enough to make it exceed, during the entire infusion process, the target pressure exerted on the infusion bag.
According to a further embodiment of the invention the infusion apparatus comprises a pump unit arranged to pump the pressure generating liquid from the third space to the second space at a controlled pumping rate. This embodiment thus constitutes an alternative to putting the pressure generating liquid in the third space under pressure. By the pump unit pumping pressure generating liquid at a controlled pumping rate a controlled flow rate of infusion liquid to the patient is also obtained.
According to still a further embodiment of the invention the infusion apparatus comprises a safety function in regard of overpressure which, when a given pressure of the infusion liquid in the confusion bag is exceeded, prevents infusion liquid from being transported along the conduit means. Such a safety function in regard of overpressure, i.a., has the advantage that, should a blocking occur in the conduit means or in a cannula connected to a patient, the safety function in regard of overpressure will be trigged. Thereby the transport of infusion liquid is stopped.
According to still a further embodiment of the invention the second portion is connected to a frame portion of the infusion apparatus by means of a joining element in such a manner, that, when a force exceeding a certain level is exerted on the second portion in at least one direction, the second portion will disengage from the frame portion, the safety function in regard of overpressure being arranged to be exerted, in combination, by the supporting means, the connecting element, the first portion, the second portion, and the joining element in combination in such a way that, if the pressure on the supporting means exceeds a certain level in spite of the supporting means, by the connecting element, having affected the first portion to reduce the load on the conduit means, the supporting means, by the connecting element, the first portion and the joining element, causes the second portion to disengage from the frame portion, making the load on the conduit means to increase again while decreasing the pressure on the supporting means. According to this embodiment a well working, relatively simple safety function in regard of overpressure is obtained.
According to a further embodiment of the invention the joining element comprises a magnet. Such a magnet can, for instance, be a permanent magnet. The permanent magnet thus holds the second portion fixed in relation to the frame portion. When a force exceeding a certain level is exerted on the second portion, the second portion will disengage from the frame portion. By the connecting element being a magnet the safety function in regard of overpressure is obtained by simple means.